Recycle fluid control in pellet impact drilling



Nov. 20, 1956 A. B. HILDEBRANDT 2,771,274

RECYCLE FLUID CONTROL IN PELLET IMPACT DRILLING Filed Oct. 28, 1953 Alexander B. Hildebrand) Inventor By Attorney United States Patent RECYCLE FLUID CONTROL IN PELLET IMPACT DRILLING Alexander B. Hildebrandt, Tulsa, Okla., assignor to Esso Research and Engineering Company, a corporation of Delaware Application October 28, 1953, Serial No. 388,756

5 Claims. (Cl. 25561) The present invention is directed to a novel form of apparatus for drilling bore holes in the earth by means of a technique known as pellet impact drilling. The invention is particularly concerned with a novel means and method for improving the efficiency of reintroducing pellets into the high-velocity fluid stream. In accordance with this invention, the paths of the recycled pellets and of a portion of the recycled fluid are separated by a deflector member that serves to overcome or minimize fluid pressure unbalance factors in the recycle zone.

The basic principles of the pellet impact technique for the drilling of bore holes in the earth involves the use of a stream of fluid pumped from the surface of the earth through a tubular member to a jet nozzle adapted to provide a high velocity jet of fluid directed downwardly toward the bottom of the bore hole. Means are provided to entrain in the high velocity fluid jet a multitude of hard, dense pellets which are accelerated to high velocity in the jet stream and thereby acquire considerable kinetic energy so that when the pellets impinge against the formation the resulting impact and fracturing forces exert a drilling action. Means are also provided for separating pellets from the tip-flowing returning stream of fluid and reintroducing the pellets into the jet stream. Preferably the pellets that are employed are smooth, non-abrasive, essentially spherical, and of substantial size, in the range of about one-eighth inch to about one inch in diameter. The basic principles of the technique of drilling by pellet impact are set forth in co-pending application Serial No. 268,873, filed by P. S. Williams on January 29, 1952, and entitled Pellet Impact Method and Apparatus.

One of the limiting factors in the efficiency of drilling by the pellet impact technique is the rate at which pellets can be recycled into the zone where they are entrained in the fluid jet. In the co-pending Williams application referred to, one disclosed method for effecting the recycling of pellets involves the use of a combination of a primary nozzle and a secondary nozzle, or mixing :chamber, having a configuration such that the bore hole annulus above the secondary nozzle is enlarged to provide a gravity settling zone where the up-flowing fluid velocity is markedly decreased. This decrease in velocity causes the pellets to separate from the circulating fluid so that they can be drawn into the secondary nozzle by a combination of gravity action and of fluid flow into the secondary nozzle, the latter action being brought about, at least in part, by the aspirating effect resulting from the passage of the fluid jet from the primary nozzle into the secondary nozzle. Experimental studies indicate that other factors, such as a random vortex action of the fluid in the vicinity of the point of entry into the secondary nozzle, also contribute to pellet recycling.

Observations of pellet action with a primary and secondary nozzle arrangement of the type described indicate that the recycled pellets become segregated roughly into two groups in the borehole annulus in the vicinity of the inlet to the secondary nozzle, one group forming a more or less stationary cloud of pellets suspended in the fluid above the secondary nozzle opening and the other group forming a circulating stream of pellets below the stationary cloud referred to. The undulating interface between the two pellet groups can serve as a deflector that directs the circulating group into the secondary nozzle entrance. However, if the interface is a considerable distance above the secondary nozzle entrance the pellet recycling action is ineflicient, whereas if the interface is too close to the secondary nozzle entrance the stationary portion of pellet presents a barrier to the circulating pellets. Variations in hole gage, fluid flow rate and other drilling factors make the control of the position of the interface and resultant efficient pellet recycling quite diflicult.

A study of the flow behavior of the fluid and pellets in the vicinity of the secondary nozzle entrance has yielded the following observations. In order that recycled fluid flowing up the bore hole annulus can be made to undergo a change in momentum so as to enter the top of the secondary nozzle, a force must be exerted on the fluid. This force must come from an unbalance of pressures at the inlet to the secondary nozzle. Contributing to this unbalance are a low pressure and a high velocity immediately above the secondary nozzle entrance and a high pressure and low velocity surrounding and slightly above the primary nozzle exit. The high pressure region in the vicinity of the primary nozzle exit tends to oppose the action of gravity that would normally cause pellets that are carried above the entrance to the secondary nozzle to pass down into the secondary nozzle. In spite of this, however, a random vortex action associated with the passage of recycled fluid into the secondary nozzle apparently creates momentary lowering of the high pressure to a degree suflicient to permit pellets to pass through the high pressure area.

The observations just discussed have led to the conclusion that more efficient recycling of pellets into the sec ondary nozzle could be attained if the recycled fluid could be directed into the secondary nozzle without appreciable throttling and if means were provided to shield the region surrounding the primary nozzle exit from fluid pressure unbalance forces.

It is one object of the present invention to provide a method and means for improving the efficiency of re-entry of pellets into the secondary nozzle or mixing chamber of a pellet impact bit. It is another object of the invention to provide a bypass path for entry of recycled fluid into the secondary nozzle of a pellet impact bit whereby the pressure unbalance that normally exists at the primary nozzle exit is materially reduced.

In accordance with this invention, a baflie member is provided at the top of the secondary nozzle, suitable ports or channels being provided on the sides of the baflles so as to permit recycled fluid to enter the secondary nozzle below the top of the baflle while directing pellets into the nozzle above the top of the batfle. In a preferred form of the invention the bafile has a solid top portion with a central opening for pellets and primary fluid and slotted sides through which a considerable portion of the recycle fluid may enter to be directed to the secondary nozzle through a path that is shielded from the primary nozzle exit zone.

A fuller understanding of the nature of the invention and of the objects to be accomplished by the invention may be obtained by referring to the accompanying drawing, in which:

Figure l is a sectional elevation of one embodiment of the invention placed in drilling position in a bore hole, the section being taken on line II of Figure 3;

Figure 2 is a cross section taken on line lI-II of Figure l; and

Figure 3 is a slightly enlarged cross section taken on line IIIIII of Figure 1.

With particular reference to details of the drawing, a

bore hole 11 is shown in which is positioned a drilling apparatus that embodies the present invention. The apparatus is supported in the bore hole on a tubular support member 12, which may be adapted for attachment to the lower end of a conventional drill pipe. The lower end'of tubular support member 12 terminates in a nozzle element 13. Supported below member 12 by means about to be described is a second tubular member having its bore in substantial alignment with the nozzle element 13. Nozzle element 13 may be referred to as a primary nozzle and tubular member 15 may be referred to as a secondary nozzle defining a centrally disposed mixing chamber 23.

In the embodiment illustrated, secondary nozzle 15 has an upper portion of reduced external diameter presenting a shoulder to which are fastened a plurality of circumferentially spaced, vertically arranged rods or bars 18 that define between them a plurality of slots 19. These slots are made narrower than the diameter of the pellets used in drilling, so that pellets will not enter the annular space 21.

Supported by and fastened to the bars .18 is a top plate member 17 having a central opening 26 that is positioned in substantial alignment with the top opening of secondary nozzle 15. Plate member 17 is fastened to and supported by tubular support member 12 by suitable means such as the three Web supporting members 16 illustrated. Plate member 17 is positioned a fixed distance above the top of secondary nozzle 15 so as to permit recycled fluid that has entered the annular space 21 through slots 19 topass from the annular space into the secondary nozzle. Preferably the underside of plate member 17 is of concave curvature to provide a deflecting surface that will direct the recycled fluid more efliciently into the secondary nozzle.

In utilizing the apparatus illustrated in the drawing, drilling is conducted much in the same manner as described in the aforementioned Williams application, fluid being pumped down the drill pipe through tubular member 12 and primary nozzle 13. The fluid leaves this nozzle in the form of a high velocity jet stream, identified as Q1, which enters secondary nozzle 15 where it combines with aspirated recycle fluid Q2G+Q2b and the total volume Q1+Q2a+Q2b passes through the secondary nozzle to impinge on the bottom of the bore hole. The circulating fluid Ql+Q2a+Q2b returns up the bore hole annulus and carries with it pellets 22 from the bottom of the bore hole. A portion of the upflowing fluid Q23 passes through the slots 19 into the annular fluid flow channel 21 and is directed into the top of the secondary nozzle by the baflle plate 17. The remaining fluid and the pellets continue on up the bore hole annulus. As the pellets reach the enlarged annulus above the top of the baffle plate 17 they lose momentum in the more slowly moving fluid stream in the enlarged annulus and then drop through the opening Zfl in the plate 17 and from thence into the secondary nozzle where the pellets again become entrained in the high velocity fluid jet issuing from the primary nozzle. A portion of the recycle fluid, Q21), is drawn into the secondary nozzle through the same path as the pellets. In the secondary nozzle the pellets attain substantially the same velocity as the fluid stream so that as they leave the lower end of the secondary nozzle they will strike against the bottom of the bore hole at a high velocity and transfer their kinetic energy to the formation. By

this action the pellets disintegrate the formation at the bottom of the borehole and thus extend the borehole further through the formation.

Because of the fact that a considerable portion of the Q2 recycle fluid, i. e., QZa, is bypassed through the slots 19 in the annular channel 21 and because of the fact that the shield 17 serves to prevent this portion of the recycled fluid from entering the zone in the vicinity of the primary nozzle, more efiicient recycling of pellets from the bore hole annulus into the secondary nozzle is attained than would be possible with a simple primary and secondary nozzle arrangement where the recycled pellets and recycled fluid must enterthe secondary nozzle through the same path.

The scope of the invention is defined by the following claims and is not to be limited merely to the specific embodiment hereinbefore described by way of example, as many obvious modifications thereof can be made without departing from the invention.

What is claimed is:

l. A drill bit assembly for drilling bore holes in the earth by entraining pellets in a high velocity stream of fluid, which comprises a jet nozzle adapted to eject a stream of fluid, an open-ended mixing chamber below the jet nozzle and a baflle member surrounding the upper end of said mixing chamber, said bafile member having a top central opening, substantially aligned with said jet nozzle and with the top opening of said mixing chamber, of suflicient size to permit the passage of pellets therethrough, and at least one side port communicating with the top opening of said mixing chamber, said side port being smaller than pellet diameter, whereby a portion of the fluid in an up-flowing stream of pellets and fluid will enter said mixing chamber through said port while pellets will be directed above the top of said battle to enter said mixing chamber through said top opening.

2. A drill bit for drilling bore holes in the earth comprising a tubular support member terminating at its lower end in a jet nozzle adapted to provide a downwardly directed high velocity jet of fluid, a second tubular member positioned below and supported by said first tubular member with its inner bore substantially aligned with said jet nozzle, and a battle member covering the top of said second tubular member, said bafile member having at least one side port establishing fluid communication between the top opening of said second tubular member and the exterior of said baflle below the top thereof, said baffle member also having a top central opening of sufficient size to permit passage of pellets therethrough, sufficient clearance being provided between said bafile mem ber and said jet nozzle to permit passage of pellets therebetween, each side port in the baflle member being of a configuration to provide passage of fluid but not of pellets.

3. Drill hit as defined by claim 2 wherein said baffle member comprises an essentially circular plate having a central opening and a plurality of circumferentially spaced, vertically arranged bars fastened at one end to the exterior of said second tubular member and the other end to said plate in a manner supporting said plate a spaced distance above said second tubular member, the spacing between said bars being less than pellet diameter, said spaces defining fluid side ports communicating with the top of said second tubular member.

4. Drill bit as defined by claim 3 wherein said second tubular member is of reduced external diameter at its top portion whereby to define with said bars an annular fluid flow channel to the top opening of said second tubular member.

5. Drill bit as defined by claim 3 wherein the underside of said circular plate is of concave curvature.

Zublin Mar. 2, 1937 Hawthorne Feb. 25, 1941 

